speed up open/close benchmark from 2 seconds to 1.2 seconds
speed up open/close benchmark from 2 seconds to 1.2 seconds

remove unnecessary FLUSH upcall from fuse

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl